Reductive Sn 2+ Compensator for Efficient and Stable Sn-Pb Mixed Perovskite Solar Cells.

Tin-lead (Sn-Pb) mixed perovskite with a narrow bandgap is an ideal candidate for single-junction solar cells approaching the Shockley-Queisser limit. However, due to the easy oxidation of Sn 2+ , the efficiency and stability of Sn-Pb mixed perovskite solar cells (PSCs) still lag far behind that of Pb-based solar cells. Herein, highly efficient and stable FA 0.5 MA 0.5 Pb 0.5 Sn 0.5 I 0.47 Br 0.03 compositional PSCs are achieved by introducing an appropriate amount of multifunctional Tin (II) oxalate (SnC 2 O 4 ). SnC 2 O 4  with compensative Sn 2+ and reductive oxalate group C 2 O 4 2- effectively passivates the cation and anion defects simultaneously, thereby leading to more n-type perovskite films. Benefitting from the energy level alignment and the suppression of bulk nonradiative recombination, the Sn-Pb mixed perovskite solar cell treated with SnC 2 O 4 achieves a power conversion efficiency of 21.43%. More importantly, chemically reductive C 2 O 4 2- effectively suppresses the notorious oxidation of Sn 2+ , leading to significant enhancement in stability. Particularly, it dramatically improves light stability.